A variety of products contain biocides to prevent their pre-mature degradation caused by microbial growth and/or to prevent unsightly appearance caused by microbial staining. Important biocides, and biocides of particular interest herein, are phenoxarsines and phenarsazines, 10,10'-oxybisphenoxarsine (OBPA) being of particular interest, and isothiazolinones, 4,5 dichloro-2-n-octyl-4-isothiazol-3-one and 2-n-octyl-4-isothiazol-3-one being of particular interest.
For ease of handling, e.g., to prevent powdered materials from diffusing into the air and creating hazardous conditions at the workplace, many biocides are packaged as concentrates. Liquid concentrates typically comprise a biocide and a solvent for a biocide, and very often contain an additional functional component, such as a plasticizer, when the biocide concentrate is to be incorporated in a plastic composition. Examples of liquid biocide concentrates are found in U.S. Pat. Nos. 4,711,914, 4,761,247, 4,891,391, and 5,498,344, the teaching of each of which are incorporated herein by reference.
Among products to which biocides are commonly added are silicone caulks. The term "caulk" is used herein broadly to include silicone elastomers useful as sealants, adhesives, etc. Most commercial silicone caulks are based on silanol-terminated polydimethyl siloxanes, although the pendant groups may be, to a greater or lesser extent, other than methyl, e.g., phenyl, cyanoethyl or trifluoropropyl. Tri- and tetra-functional silanes serve as cross-linking agents, the functional organic groups of such silanes being, for example, alcohols, carboxylic acids, amines, ketoximines, aldoximes, and amides. Acetic acid, is the most common functional group of cross-linking silanes; dissociation of the acetic acid group from the silane during curing being responsible for the vinegar smell associated with many such caulks. Accordingly, where odor is of concern, silanes with other functional groups, such as ketoximes (e.g., methylethylketoxime) are used. Caulks generally contain fillers, such as silica. In two-part caulks, a condensation catalyst, such as a tin soap, is contained in a part separate from the polysiloxane. One-part caulks are produced in entirely anhydrous conditions and rely on diffusion of moisture from the air to effect a cure. One-part caulks may rely entirely on moisture to effect a cure, but in some cases may contain a condensation catalyst. Both two-part and one-part silicone caulks undergo room temperature vulcanization (RTV).
Currently, a biocide concentrate for silicone caulks comprises OBPA as the biocide, nonylphenol as the solvent, and a silicone oil, particularly poly(dimethyl siloxane). The poly(dimethyl siloxane) acts to compatibilize the biocide with the polysiloxane of the caulking composition to which it is added. Some silicone caulk producers use a composition comprising OBPA, isodecanol and the plasticizer di-(2-ethyl hexyl) phthalate. 2-ethyl-1,3-hexanediol has also been used as an OBPA solvent in silicone caulks. In such compositions, the solvents and any plasticizer are non-volatile and remain in the silicone caulk as it cures. The solvents and di-(2-ethyl hexyl), however, are viewed as adulterants, having uncertain effects on the final product. Nonylphenol yellows some compounds upon exposure to sunlight.
Many biocides, such as OBPA 4,5 dichloro-2-n-octyl-4-isothiazol-3-one and, 2-n-octyl-4-isothiazol-3-one have low solubility in many organic solvents. Furthermore, selection of appropriate solvents is complicated because (1) the solvent cannot interfere with the RTV reaction; (2) the oligomers used in the caulk are somewhat viscous (3) the aesthetic properties of the caulk, such as color and odor are important, and (4) there are many formulators of proprietary caulk formulas with a wide range of formulas to satisfy different physical property requirements such as flexibility, white-pigmented, adhesion to glass, metal, etc. It has proven difficult to find a solvent for anti-microbials that does not detract from one or another desired attribute discussed above. Also, it is not common in the silicone caulk industry to add volatile compounds, with the exception of the functional groups of the silane which volatalize during the room temperature vulcanization.